Automatic choke



Feb. 10, 1970 AUTOMATIC CHOKE Filed March 21, 1968 I6 L 7 T L ll;

I0 FIG. I

4 INVENTOR DWIGHT M. GORDON BYW/ZI/4% ATTORNEY D. M. GCRDON 3,494,598

United States Patent O 3,494,598 AUTOMATIC CHOKE Dwight M. Gordon,Farmington, Mich., assignor to ACF Industries, Incorporated, New York,N.Y., a corporation of New Jersey Filed Mar. 21, 1968, Ser. No. 715,065Int. Cl. F02m 1/10 US. Cl. 261-39 6 Claims ABSTRACT OF THE DISCLOSURE Anautomatic choke of a carburetor includes a sector arm fixed to the chokevalve shaft, and a first rod connected to a suction motor at one end andhaving an opposite bent end in an arcuate slot of the sector arm. Aspring anchored to the sector arm engages the first rod, and the springis biased to close the choke when the engine is not running and,consequently, the suction motor is not operated. The sector arm isconnected by a second rod to a thermostat spring arranged to close thechoke at low temperatures and open it at high temperatures. At ratherhigh ambient temperatures, when the thermostat would not close thechoke, the first mentioned spring closes the choke to facilitatestarting the engine.

BACKGROUND OF THE INVENTION In an automatic choke arrangement, includinga suction motor, for opening an unbalanced choke valve immediately afterengine starting, the thermostat spring should not present such a highchoke closing bias that the opening of the choke is delayed too long,otherwise the engine will run with an overly rich mixture. When thethermostat closing bias is reduced to allow the choke to open shortlyafter engine starting at normal or low temperatures, the thermostat maynot close the choke at rather high ambient temperatures. But an openchoke will give an undesirably lean mixture for engine starting, even athigh ambient temperatures of, say, 90 degrees Fahrenheit. It is anobject of the invention to avoid this difiiculty by maintaining thechoke closed during engine starting, while keeping the closing bias ofthe thermostat spring low enough to permit quick partial opening of thechoke after engine starting.

Examples of particular conditions can be cited when it is desirable toclose the choke valve even though underhood temperatures may berelatively high. In some types of carburetors fuel enters theaccelerating pump over a weir in the upper portion of the pump cylinder.With such an accelerator pump construction, if the car has been drivento normal operating temperatures and is then parked over night orlonger, it can be expected that all of the fuel in the pump cylinderwill boil out and the cylinder will be dry or substantially dry. Thenupon attempting to start the car the normal practice is to step down theaccelerator pedal one time and then turn the ignition key. This one shotfrom the accelerating pump should be sufficient to allow the engine tofire, but under the circumstances described since no fuel is present theengine would not fire and might not start at all.

Another example is the situation where the car has been driven and hasbecome somewhat stabilized in temperature and then is parked for arelatively short time, such as approximately one hour. In this length oftime the accelerating pump cylinder can boil out or nearly boil out andyet the thermostatic coil will have a relatively high temperature andwill be exerting only a partial closing bias on the choke valve. Underthese circumstances cranking would not produce enough vacuum under thechoke to draw fuel out of the main fuel nozzle 3,494,598 Patented Feb.10, 1970 and at the same time the accelerating pump would not have madeits initial discharge as would normally be expected. Here, again, thefull closing of the choke provided by the invention is very desirable.

SUMMARY OF THE INVENTION A carburetor is provided having an unbalancedchoke valve connected to the thermostat spring, as is conventional. Anarcuately slotted sector arm is fixed to the choke valve shaft and a rodconnects the sector plate to the thermostat spring. A suction motorresponsive to intake manifold pressure is linked to a rod having a bentend extending into the arcuate slot, so that the bent end of the rod canride in the slot when the sector arm is turned by the thermostat springto open the choke. Before the engine starts, the end of the rod ispositioned a short distance from the end of the arcuate slot to providea predetermined lost motion between the suction motor and the sector armfixed to the choke valve. A closure spring fixed to the sector arm bearsagainst the rod so as to bias the choke closed when the engine is notrunning. When the engine starts the suction begins to operate andrelaxes the closure spring, and the unbalanced choke valve, due to itsweight, opens to a degree dependent on the ambient temperature sensed bythe thermostat spring, and then opens further as the suction motor movesthe sector arm directly.

BRIEF DESCRIPTION OF THE DRAWING The invention will be fully understoodfrom the following description and the drawing, wherein:

FIG. 1 is a plan view, partly in section of a carburetor, showing thechoke actuating mechanism constituting the invention.

FIGS. 2 and 3 are partial views of tWo modifications of the structureshown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, anembodiment of the invention is illustrated comprising a carburetor 10,the upper end 12 of which is adapted to be fitted to an air filter andthe lower end 14 connected to the engine intake manifold. In the airhorn 16 of the carburetor is the conventional throttle valve on shaft 18and unbalanced choke valve 20 on shaft 22. Sector shaped arm 24 is fixedon shaft 22 and has an arcuate slot 26. Rod 28 connects arm 24 tothermostatic coil spring 30. Rod 32 has a bent end 33 extending throughslot 26, a looped portion 34, and a re mote end attached to plunger 36of diaphragm suction motor 38. A torsion spring 40 wrapped round shaft22 has one end 42 fixed to arm 24 and another end 44 abutting portion 34of rod 32. Nipple 46 of suction motor 38 is adaped to receive a conduitconnected downstream of the throttle, or effectively to the intakemanifold.

Thermostat spring 30 is normally designed to hold choke 20 closed atcold temperatures and to open the choke at elevated temperatures. Forreasons already set forth, the thermostat itself may not cause closingof choke 20 during engine cranking under conditions when choke closingis desirable or even necessary. When cold, spring 30 contracts, raisesrod 28 and tends to close choke 20, and during heating spring 30expands, pulls rod 28 down and tends to open the choke. Before theengine starts suction motor 38 is inoperative and hence its diaphragmand plunger 36 are in their uppermost positions. End 33 of rod 32 isthen spaced from the right hand end of arcuate slot 26, as indicated at48. Since end 44 of spring 40 is cocked against rod 32, the other end 42of spring 40 acts on arm 24 to turn it counterclockwise and close choke20, even though the thermostat may be at a temperature which will notcause it, of itself, to quite close the choke. Torsion spring 40 needslittle force to act against the relaxed thermostat spring 30sufficiently, or overcome the unbalanced weight of the choke valve, inorder to hold the choke closed before the engine starts. After theengine starts, suction motor 38 begins to operate and move plunger 36and rod 32 downward, thereby relieving the pressure on the end 44 ofspring 40, so that the latter no longer urges the choke closed. Due tothe unbalanced nature of choke 20, it is opened by gravity and thehigher pressure on its top side when spring 40 relaxes. As the enginecontinues running suction motor 38 pulls rod 32 down and turns sectorarm 24 to open choke 20 further, to a predetermined degree. Thereafter,the opening of the choke can proceed still further as the engine heatsup and thermostat spring 30 pulls rod 28 downward. As sector shaped arm24 turns with the choke, the end 33 of rod 22 rides in slot 26. It canbe seen then, that even when thermostat 30 is at such a temperature thatit would not close the choke, the choke is closed by torsion spring 40,to facilitate starting, and proper operation is obtained after enginestarting.

In FIG. 2 there is shown a modified torsion spring 50 and its connectionto rod 51, which differs from rod 32 in that there is no bent portion34. The end 52 of spring 50 is anchored to sector arm 53 and end 54 ofthe spring is looped round rod 51. The latter is spaced from the end ofarcuate slot 55 as indicated at 48 in FIG. 1, when rod 51 is in itsnormal non-operated position, so that initially there is a lost motionbetween rod 51 and sector arm 53. It will be evident that the structureof FIG. 2 functions in substantially the same manner as that of FIG. 1.

FIG. 3 shows another type of choke closing spring. Spring 60 is a bowed,preferably flat spring fixed to arm 62 by screws 63, 64. Rod 66 has abent end 67 spaced from the end of arcuate slot 68 when the rod is inits non-operated position. In this position of rod 66, a bend 70 thereofbears against spring 60 to urge choke valve 20 closed. As rod 66 movesdownward in response to engine starting, the pressure on spring 60 isrelieved, allowing choke valve 20 to open, as a result of its weight. Asrod 66 moves down further, the end 67 thereof reaches the end of slot68, and thereafter moves arm 62 along with it, and opens choke 20further. It will be understood, although connection to the thermostat isnot shown, that choke valve shaft 22 is actuated by a thermostat inessentially the same manner as in FIG. 1, and the operation of the chokeotherwise is like that of FIG. 1.

I claim:

1. In a carburetor having an automatic choke including an unbalancedchoke valve; a thermostat connected to said choke valve for positioningthe same in response to temperature so that the choke valve is notclosed by the thermostat when it is above a predetermined temperature; asuction motor adapted to be actuated in response to intake manifoldpressure and having linkage providing a lost motion connection to thechoke valve, the improvement comprising spring means connected to saidchoke valve and tensioned for closing the same even when said thermostatis above said predetermined temperature, said spring means engaging saidlinkage and being arranged so that actuation of said suction motorproduces a limited lost motion travel of said linkage in a direction toreduce the tension of the spring means to enable the choke valve to beopened by the thermostat above said predetermined temperature.

2. The invention according to claim 1, wherein said spring means is atorsion spring having one end fixed to said choke valve and its otherend in engagement with said linkage.

3. The invention according to claim 2, wherein said choke valve has apivot shaft and an arm fixed to said shaft, said arm having a slot, saidlinkage including a rod connected to and actuated by the suction motorand having a remote end extending into said slot to form said lostmotion connection, said other end of the torsion spring being normallypressed against said rod.

4. The invention according to claim 3, wherein said other end of thetorsion spring is connected to the remote end of said rod.

5. The invention according to claim 1, wherein said spring means is afiat spring having at least one end thereof fixed to said choke valveand another portion thereof in engagement with the suction motorlinkage.

6. The invention according to claim 5, wherein said choke valve is anunbalanced valve having a pivot shaft and an arm fixed to said shaft,said spring being a bowed spring having both ends thereof fixed to saidarm and an intermediate portion engaging said linkage.

References Cited UNITED STATES PATENTS 2,998,233 8/ 1961 Marsee.3,167,254 1/ 1965 Goodyear. 3,253,781 5/ 1966 Schefl'ler. 3,284,06111/1966 Gordon. 3,321,193 5/1967 Highley.

TIM R. MILES, Primary Examiner

